Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended		149 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020
Class of Stock [Line Items]
Shares repurchased	1,709,431	4,890,155	58,588,409
Average purchase price per share	$ 87.87	$ 102.25	$ 73.44
Shares repurchased (in $ millions)	$ 150	$ 500	$ 4,303
Aggregate Board of Directors repurchase authorizations (in $ millions)	$ 0	$ 1,500	$ 5,366